linux-kernel - Re: [PATCH v5 9/9] drm/vc4: hdmi: use drm_atomic_helper_connector_hdmi_update

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Message-ID: <ae24x2bo736jpzi77l34hybejawwe4rp47v2idedga344ye6zr@bxsxz34dwrd2>
Date: Tue, 3 Dec 2024 14:27:44 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Maxime Ripard <mripard@...nel.org>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
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	Inki Dae <inki.dae@...sung.com>, Seung-Woo Kim <sw0312.kim@...sung.com>, 
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	Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>, Jani Nikula <jani.nikula@...ux.intel.com>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, linux-sound@...r.kernel.org, 
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Subject: Re: [PATCH v5 9/9] drm/vc4: hdmi: use
 drm_atomic_helper_connector_hdmi_update_edid()

On Mon, Dec 02, 2024 at 02:27:49PM +0100, Maxime Ripard wrote:
> Hi,
> 
> On Sun, Dec 01, 2024 at 02:44:13AM +0200, Dmitry Baryshkov wrote:
> > Use the helper function to update the connector's information. This
> > makes sure that HDMI-related events are handled in a generic way.
> > Currently it is limited to the HDMI state reporting to the sound system.
> > 
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > ---
> >  drivers/gpu/drm/vc4/vc4_hdmi.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > index d0a9aff7ad43016647493263c00d593296a1e3ad..d83f587ab69f4b8f7d5c37a00777f11da8301bc1 100644
> > --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > @@ -401,13 +401,16 @@ static void vc4_hdmi_handle_hotplug(struct vc4_hdmi *vc4_hdmi,
> >  	 */
> >  
> >  	if (status == connector_status_disconnected) {
> > +		drm_atomic_helper_connector_hdmi_update_edid(connector, NULL);
> >  		cec_phys_addr_invalidate(vc4_hdmi->cec_adap);
> >  		return;
> >  	}
> >  
> >  	drm_edid = drm_edid_read_ddc(connector, vc4_hdmi->ddc);
> >  
> > -	drm_edid_connector_update(connector, drm_edid);
> > +	// TODO: use drm_atomic_helper_connector_hdmi_update() once it gains
> > +	// CEC support
> > +	drm_atomic_helper_connector_hdmi_update_edid(connector, drm_edid);
> 
> So, it's not just about EDID, and I think we shouldn't really focus on
> that either.
> 
> As that patch points out, even if we only consider EDID's, we have
> different path depending on the connector status. It shouldn't be up to
> the drivers to get this right.
> 
> What I had in mind was something like a
> drm_atomic_helper_connector_hdmi_hotplug function that would obviously
> deal with EDID only here, but would expand to CEC, scrambling, etc.
> later on.

I thought about it, after our discussion, but in the end I had to
implement the EDID-specific function, using edid == NULL as
"disconnected" event. The issue is pretty simple: there is no standard
way to get EDID from the connector. The devices can call
drm_edid_read(), drm_edid_read_ddc(connector->ddc) or (especially
embedded bridges) use drm_edid_read_custom().

Of course we can go with the functional way and add the
.read_edid(drm_connector) callback to the HDMI funcs. Then the
drm_atomic_helper_connector_hdmi_hotplug() function can read EDID on its
own.

Also the function that you proposed perfectly fits the HPD notification
callbacks, but which function should be called from the .get_modes()?
The _hdmi_hotplug() doesn't fit there. Do we still end up with both
drm_atomic_helper_connector_hdmi_hotplug() and
drm_atomic_helper_connector_hdmi_update_edid()?

> 
> And would cover both the connected/disconnected cases.
> 
> Maxime



-- 
With best wishes
Dmitry